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41.
Sigurd Schulz Wolfgang Kaiser Günther Breuel 《International Review of Hydrobiology》1991,76(3):351-359
Eutrophication of the nature is one of the most relevant problems for the human society today. In comparison to terrestrial and limnological ecosystems, however, the marine environment is affected with some exceptions of coastal waters in a minor degree. On the basis of data from 1976–1988 trend analysis for chlorophyll, primary production, zooplankton biomass and water transparency have been carried out for the Mecklenburg Bight and different areas of the Baltic proper. As expected from the longterm increase in the nutrient levels, also for some pelagic biological variables increasing trends could be observed. At least for chlorophyll they are significant in the 95% probability level for all investigated areas. Primary production shows also an increase, however, not significant for each subarea. For zooplankton nearly no changes could be observed. All data reflect a high interannual variability, which can partly be explained by meteorological and oceanological conditions. The results are discussed from an ecological point of view. The increase in phytoplankton variables is considered to be at least partly related to the eutrophication of the Baltic. 相似文献
42.
Richard Ward Christos Pliotas Emma Branigan Christian Hacker Akiko Rasmussen Gregor Hagelueken Ian R. Booth Samantha Miller John Lucocq James H. Naismith Olav Schiemann 《Biophysical journal》2014
Mechanosensitive channel proteins are important safety valves against osmotic shock in bacteria, and are involved in sensing touch and sound waves in higher organisms. The mechanosensitive channel of small conductance (MscS) has been extensively studied. Pulsed electron-electron double resonance (PELDOR or DEER) of detergent-solubilized protein confirms that as seen in the crystal structure, the outer ring of transmembrane helices do not pack against the pore-forming helices, creating an apparent void. The relevance of this void to the functional form of MscS in the bilayer is the subject of debate. Here, we report PELDOR measurements of MscS reconstituted into two lipid bilayer systems: nanodiscs and bicelles. The distance measurements from multiple mutants derived from the PELDOR data are consistent with the detergent-solution arrangement of the protein. We conclude, therefore, that the relative positioning of the transmembrane helices is preserved in mimics of the cell bilayer, and that the apparent voids are not an artifact of detergent solution but a property of the protein that will have to be accounted for in any molecular mechanism of gating. 相似文献
43.
Anne Sverdrup-Thygeson Olav Skarpaas Frode Ødegaard 《Biodiversity and Conservation》2010,19(3):837-852
In this study we investigated hollow oaks (Quercus robur, Q. petrea) situated in open landscapes and in forests in Norway in northern Europe, and compared their importance for rare and threatened beetles (Coleoptera). Old, hollow oak trees, both in parks and in forests, were extremely rich in red-listed beetles, and hosted a high proportion of threatened species. The proportion of oak associated species and the mean number of red-listed beetle species per tree was similar in the two site types, but rarefaction showed that for a certain number of individuals, oaks in forests had more threatened and near-threatened species than oaks in parks. The species composition also differed between site types: Park oaks had a higher proportion of species associated with hollows and animal nests, whereas in forests, there was a higher proportion of species depending on dead oak wood in general. Four factors were significant in explaining the richness of red-listed beetles in our study: Tree circumference, cavity decay stage, proportion of oak in the surroundings, and coarse woody debris (CWD) in the surroundings. Forest oaks were smaller, but they still trapped a species richness comparable to that of the larger park oaks—probably a result of high amounts of CWD in the surroundings. We show that oaks in open landscapes and oaks in forest have only partly overlapping beetle assemblages and, thus, cannot be substituted in conservation. Planning for conservation of red-listed beetles associated with this key habitat demands a large scale perspective, both in space and time, as the surroundings have important effects on associated threatened and near threatened species. 相似文献
44.
Microbial Community in Black Rust Exposed to Hot Ridge Flank Crustal Fluids 总被引:1,自引:0,他引:1 下载免费PDF全文
Satoshi Nakagawa Fumio Inagaki Yohey Suzuki Bjrn Olav Steinsbu Mark Alexander Lever Ken Takai Bert Engelen Yoshihiko Sako Charles Geoffrey Wheat Koki Horikoshi Integrated Ocean Drilling Program Expedition Scientists 《Applied microbiology》2006,72(10):6789-6799
During Integrated Ocean Drilling Program Expedition 301, we obtained a sample of black rust from a circulation obviation retrofit kit (CORK) observatory at a borehole on the eastern flank of Juan de Fuca Ridge. Due to overpressure, the CORK had failed to seal the borehole. Hot fluids from oceanic crust had discharged to the overlying bottom seawater and resulted in the formation of black rust analogous to a hydrothermal chimney deposit. Both culture-dependent and culture-independent analyses indicated that the black-rust-associated community differed from communities reported from other microbial habitats, including hydrothermal vents at seafloor spreading centers, while it shared phylotypes with communities previously detected in crustal fluids from the same borehole. The most frequently retrieved sequences of bacterial and archaeal 16S rRNA genes were related to the genera Ammonifex and Methanothermococcus, respectively. Most phylotypes, including phylotypes previously detected in crustal fluids, were isolated in pure culture, and their metabolic traits were determined. Quantification of the dissimilatory sulfite reductase (dsrAB) genes, together with stable sulfur isotopic and electron microscopic analyses, strongly suggested the prevalence of sulfate reduction, potentially by the Ammonifex group of bacteria. Stable carbon isotopic analyses suggested that the bulk of the microbial community was trophically reliant upon photosynthesis-derived organic matter. This report provides important insights into the phylogenetic, physiological, and trophic characteristics of subseafloor microbial ecosystems in warm ridge flank crusts. 相似文献
45.
Moose selecting for specific nutritional composition of birch places limits on food acceptability 下载免费PDF全文
Hilde K. Wam Annika M. Felton Caroline Stolter Line Nybakken Olav Hjeljord 《Ecology and evolution》2018,8(2):1117-1130
Despite decades of intense research, it remains largely unsolved which nutritional factors underpin food selection by large herbivores in the wild. We measured nutritional composition of birch foliage (Betula pubescens) available to, and used by, moose (Alces alces) in natural settings in two neighboring regions with contrasting animal body mass. This readily available food source is a staple food item in the diet of moose in the high‐fitness region, but apparently underutilized by moose in the low‐fitness region. Available birch foliage in the two regions had similar concentrations of macronutrients (crude protein [CP], fiber fractions, and water‐soluble carbohydrates [WSC]), although a notably lower variation of WSC in the low‐fitness region. For minerals, there were several area differences: available birch foliage in the low‐fitness region had less Mg (depending on year) and P, but more Ca, Zn, Cu, and Mn. It also had higher concentrations of some plant secondary metabolites: chlorogenic acids, quercetins, and especially MeOH‐soluble condensed tannins. Despite the area differences in available foliage, we found the same nutritional composition of birch foliage used in the two regions. Compared to available birch foliage, moose consistently used birch foliage with more CP, more structural fiber (mainly hemicellulose), less WSC, higher concentrations of several minerals (Ca, Zn, K, Mn, Cu), and lower concentrations of some secondary metabolites (most importantly, MeOH‐soluble condensed tannins). Our study conceptually supports the nutrient‐balancing hypothesis for a large herbivore: within a given temporal frame, moose select for plant material that matches a specific nutritional composition. As our data illustrate, different moose populations may select for the same composition even when the nutritional composition available in a given food source varies between their living areas. Such fastidiousness limits the proportion of available food that is acceptable to the animal and has bearings on our understanding and application of the concept of carrying capacity. 相似文献
46.
Morten Glasø Olav Hilmar Iversen Torstein Hovig 《Virchows Archiv. B, Cell pathology including molecular pathology》1988,56(1):221-235
The nature and significance of so-called dark keratinocytes in the epidermis during chemical carcinogenesis is still a matter
of concern and debate. Based on ultrastructural observations it has been suggested that dark cells most often are shrunken
cells. Reports on skin carcinogenesis, however, claim that dark cells are a sign of ongoing tumor promotion and represent
those stem cells in the epidermis from which the tumors originate. It is therefore important to find out whether these cells
are simply injured and shrunken cells, or vital cells of great importance for carcinogenesis. Dark cells are assumed to be
rich in ribosomes. There is evidence, however, that the observed number of dark cells is highly dependent on tissue fixation.
In the present ultrastructural study, morphometric methods were used to compare the effects of two different fixation procedures
on the amount of cytoplasmic ribosomes in dark cells from both untreated and carcinogen-treated hairless mouse epidermis.
The results show that the ultrastructural features of both dark and clear cells vary considerably with different fixation
procedures. In acetone-treated controls typical dark cells are only observed when the fixative has a lower osmotic activity
than the plasma. With iso-osmolal fixation typical dark cells are not observed. After an abortive two-stage carcinogenesis
treatment, in which a single application of 9,10-dimethyl-l,2-benzanthracene (DMBA) in acetone was followed by a single application
of 12-O-tetradecanoyl-13-acetate (TPA) in acetone, signs of cell injury could be found after both fixation procedures. With
DMBA/TPA and hypo-osmolal fixation the number of dark cells seemed to increase, whereas only signs of cell injury with occurrence
of some heavily altered “clear cells” dominated the picture with iso-osmolal fixation. Morphometry showed that both the numerical
and the volumetric densities of cytoplasmic ribosomes in basal keratinocytes varied most significantly with the fixation procedure
used. The cytoplasmic volumes did not vary in a way that could explain these differences. One might therefore assume that
the number of ribosomes depends on the fixative. Large swelling artifacts occurred when a fixative with low osmotic activity
was used, leading to compression of neighboring cells. Hence, an increased ribosomal density reported previously in dark cells
is probably related to such cell volume artifacts and does not reflect an actually increased quantity of ribosomes. With both
fixation procedures, a single application of DMBA followed by one of TPA appeared to produce an increased number of ribosomes
in basal keratinocytes. When hypo-osmolal fixation was used, however, treatment with DMBA/TPA did not influence the cytoplasmic
volume or the numerical density of ribosomes, in dark cells. This might indicate that so-called dark keratinocytes following
DMBA/TPA treatment are functionally inactive cells that appear more vulnerable than active cells to compression during hypo-osmolal
fixation. 相似文献
47.
48.
Association between the gene encoding 5-lipoxygenase-activating protein and stroke replicated in a Scottish population 总被引:6,自引:0,他引:6 下载免费PDF全文
Helgadottir A Gretarsdottir S St Clair D Manolescu A Cheung J Thorleifsson G Pasdar A Grant SF Whalley LJ Hakonarson H Thorsteinsdottir U Kong A Gulcher J Stefansson K MacLeod MJ 《American journal of human genetics》2005,76(3):505-509
Cardiovascular diseases, including myocardial infarction (MI) and stroke, most often occur on the background of atherosclerosis, a condition attributed to the interactions between multiple genetic and environmental risk factors. We recently reported a linkage and association study of MI and stroke that yielded a genetic variant, HapA, in the gene encoding 5-lipoxygenase-activating protein (ALOX5AP), that associates with both diseases in Iceland. We also described another ALOX5AP variant, HapB, that associates with MI in England. To further assess the contribution of the ALOX5AP variants to cardiovascular diseases in a population outside Iceland, we genotyped seven single-nucleotide polymorphisms that define both HapA and HapB from 450 patients with ischemic stroke and 710 controls from Aberdeenshire, Scotland. The Icelandic at-risk haplotype, HapA, had significantly greater frequency in Scottish patients than in controls. The carrier frequency in patients and controls was 33.4% and 26.4%, respectively, which resulted in a relative risk of 1.36, under the assumption of a multiplicative model (P=.007). We did not detect association between HapB and ischemic stroke in the Scottish cohort. However, we observed that HapB was overrepresented in male patients. This replication of haplotype association with stroke in a population outside Iceland further supports a role for ALOX5AP in cardiovascular diseases. 相似文献
49.
Gerard C. Van Stein Gerard Van Koten Hans Passenier Olav Steinebach Kees Vrieze 《Inorganica chimica acta》1984,89(2):79-87
The reactions of the dianionic [(pyrrole-2-CHN)2R]2? ligands [(N′2N2)2?] (R = (R)(S)-1,2-cyclohexane or 1,2-ethane) with Zn(II) yield neutral dimeric [Zn2(N′2N2)2] complexes. The dimeric nature of the complexes was established by field-desorption mass spectrometry. 1H NMR studies show that these complexes have dimeric structures in solution in which the (N′2N2)2? ligands act as di-bidentates.The metal centres have tetrahedral geometries and bot have Δ or Λ configurations. The complex with the (R)(S)-1,2-cyclohexanediyl bridges has a rigid structure in solution. Neither intermolecular nor intramolecular exchange processes are observed The 1H NMR spectrum of the complex with the 1,2-ethanediyl bridging groups shows that at 213 K in CDCl3 a fast conformational movement is already taking place between two identical structures of the complex. It is not possible to determine whether in this complex intermolecular exchange processes are also taking place.The reactions of the anionic [pyrrole-2-CHNR′]? ligands [(N′N)?] (R′ = t-Bu, i-Pr, (S)-CHMePh or 2,6-xylyl) with Zn(II) yield the neutral Zn(N′N)2 complexes. These complexes were synthesized to study the coordination properties of the [pyrrole-2-CHNR′]? moieties with Zn(II). A 1H NMR study established that the zinc centres in the complexes containing the prochiral i-Pr or chiral (S)-CHMePh substituents have tetrahedral geometries with Δ or Λ configurations in CDCl3 at 213 K. These complexes undergo an intramolecular exchange process at higher temperatures (above 260 K when R′ = i-Pr) which involves inversion of the configuration of the zinc centre. A mechanism for this exchange process is proposed. 相似文献
50.
After a marked decline at the beginning of the 1900s, the arctic fox Alopex lagopus population in Fennoscandia has remained at a very low level. We suggest that the main cause for the population crash was
winter starvation caused by (1) over-hunting of reindeer Rangifer tarandus populations, and thus reduced carcass availability in the mountains, and (2) increased interspecific competition for these
carcasses because of increased invasion of red foxes Vulpes vulpes from lower altitudes. The failure of arctic fox populations to recover, despite increasing reindeer populations in the mid
1900s, can be explained by a concurrent strong increase in red fox numbers. Analyses of countywide hunting statistics from
Norway 1891–1920 suggest that there actually was an increase in red fox numbers in the period of arctic fox decline, and that
the increase in reindeer populations from the 1920s to the 1950s was accompanied by a new increase in red fox numbers. We
conclude that restoring arctic fox populations most likely will require a substantial and lasting reduction of red fox populations. 相似文献